An interlock control of that type is known in particular from French patent application 89 13279. The circuit-breaker comprises two main contacts, of which one is fixed and the other is moving, and two arcing contacts of which one is fixed and the other is moving. Pneumatic valves control displacement of the moving contacts to open or close the circuit-breaker. The disconnector comprises a contact rod which is movable relative to the two fixed contacts, and whose displacement is controlled by another pneumatic valve to disconnect or interconnect the two fixed contacts. The pneumatic valves are provided with electrically-controlled valves that are controlled by sophisticated electronics to ensure that the disconnector opens after the circuit-breaker, and that the circuit-breaker closes after the disconnector.